There are known fixed caliper disc-brakes in which a caliper body comprises two walls arranged on both sides of the brake disc and connected to each other by means of two or more connecting bridges which straddle the disc. Typically, the two walls are joined together by connecting screws accommodated inside the connecting bridges. The wall of the caliper body facing towards the inside of the vehicle comprises two holes to accommodate respective attachment screws to attach the caliper body to the vehicle suspension so that it is integral in rotation and in translation. In both walls of the caliper body a seating is made to accommodate a pad having a lining of friction material facing towards the brake disc and at least one of the walls delimits one or more seatings for hydraulic cylinder/piston units capable of clamping the pads against the brake disc to generate the braking force.
During braking, the body of a fixed caliper is subjected to a highly complex system of forces. The force of reaction to the axial clamping of the disc involves an axial tensile force in the connecting bridges, a bending moment in the walls about an axis substantially radial relative to the axis of rotation of the brake disc and a bending moment of reaction in the connecting bridges, which is also substantially about an axis substantially radial to the axis of rotation of the disc.
The braking force transmitted by friction from the brake disc to the pads and from these through the caliper body to the vehicle suspension involves further torsional and shear loads on the caliper body. The result of this, in addition to a large shear force, is a further bending moment in the connecting bridges. This state of three-dimensional loads on the caliper body during braking results in substantial deformation and distortion of the body. This means that it is necessary to oversize both the caliper body itself and the suspension at the points at which the caliper is attached in order to prevent relative axial motion of the two attachment points so as to limit the distortion of the caliper body.
Adequate dimensioning of the caliper means that it must be large in size to contain the deformation within the predefined limits.
While calipers of the floating type, supported so that they can slide axially and subjected to a simpler state of force and deformation, are able to compensate for deformation by means of relative motion of the attachment points along the sliding pins, the tendency towards excessive distortion of fixed calipers is manifested in overloading of the suspension, a risk of the pads becoming jammed or wedged and uneven wear of the friction lining of the pads.
The purpose of the present invention is therefore to make available a fixed caliper which can be secured axially to a vehicle at two or more points having characteristics such as to obviate the disadvantages cited with reference to the known technology.